Here's the skinny.
Back in 2015 ANZ did a $2.5B capital raising to increase its cash reserves. ANZ arranged for Citigroup, Deutsche Bank and JP Morgan to underwrite the share issue. That means they agreed to buy any shares issued in the capital raising that other investors didn't buy.
It turns out around a third of the shares didn't sell, so Citi, Deutsche and JP Morgan had to buy them. The criminal cartel case alleges that they then got together and agreed to limit or restrict their disposal of the shares.
In a scenario like that, the company issuing the shares would have an interest in such a sizeable chunk of shares not being offered into the market too quickly, as this oversupply could negatively impact the prevailing share price on the ASX.
Next, law. Cartel conduct occurs in a few different ways. In this case, based on the limited facts that have been reported, there could be a couple of options.
If competitors make an arrangement with the purpose or effect of fixing or maintaining prices, like share prices, then that's cartel conduct.
If competitors make an arrangement with the purpose of limiting supply of goods or services, like shares, that's also cartel conduct.
ANZ supplied the shares in this case, so it might be on the hook for inducing the cartel conduct, rather than being a competitor of Citi, Deutsche and JP Morgan. JP Morgan has apparently been granted immunity for dobbing to the ACCC.
The ACCC can prosecute cartel conduct as a civil contravention itself, or it can pass a case to the DPP to prosecute as a criminal offence. The corporate fines are the same, but there can be up to 10 years' jail time for individuals. In this case the DPP is prosecuting criminal offences.
The DPP will have to prove its case to the criminal standard, i.e. beyond reasonable doubt. Pursuing the criminal prosecution rather than a civil action suggests that the ACCC is confident.
If they're right, the penalties could be massive. The maximum is the greater of $10M, 3 times the value of the benefit derived, or 10% of the company's annual turnover in the year prior to the contravention. However you look at it, those would be big numbers.
On the flip side, if the case fails then there will be pie on the ACCC's face, especially when it might have had an easier time pursuing the civil action. So much pie.